A retired detective garda has been found guilty of lying to Garda Siochana Ombudsman Commission officers who were investigating the posting of a Valentine's day card containing a bullet, a thong and a "raunchy" poem.

David O'Brien (52) was fined €500 for making a false statement to the Garda watchdog.

O'Brien was a member of the "cold case" Serious Crime Review Team at Harcourt Square when he committed the crime. He has since left the force.

Dublin District Court heard a woman O'Brien knew allegedly mailed the envelope. When the Garda Siochana Ombudsman Commission (GSOC) interviewed him, he claimed he had not been in touch with her since the 1990s.

However, the court heard the pair had exchanged hundreds of calls and texts before and after the package was allegedly sent.

O'Brien had pleaded not guilty to giving false or misleading information to GSOC on September 10, 2012.

During the trial, the court heard nearly 300 calls and texts were exchanged between two phones linked to the pair over the course of eight weeks.

Some 291 communications passed between the phones between February 1, 2011, and March 26, 2011. A total of 187 calls and texts were sent from O'Brien's phone, with 104 returned from the other phone.

Package

Detective Sergeant Michael Buckley received the package at his workplace where O'Brien worked under him. O'Brien denied any involvement and said he had not spoken to the woman who allegedly sent the envelope in 15 to 20 years.

The GSOC complaint was made by Det Sgt Buckley's wife Briege, who claimed her husband was being bullied and intimidated.

She felt the bullet was a threat to her and her two sons.

Defence barrister Kathleen Leader BL said the prosecution had admitted that the evidence in relation to the woman's phone was "not strong."

There was no evidence from anybody that the phone was attributable to the woman in the time frame in question, Ms Leader said.

She argued there were "reasonable possibilities" for the use of the woman's phone in 2011.

"She could have given it to her child, she could have lost it, there is any number of possibilities," Ms Leader said.

Judge Smyth said: "Sending a card with a raunchy poem and a thong? Is that something somebody would do for somebody they hadn't met since the 1990s? I don't know, I'm just throwing it out there."

The court heard O'Brien had no previous convictions.

He had joined the gardai in 1983 and retired in March 2015, Ms Leader said.

He spent most of his time in the Dublin North Central area before joining the cold case unit in 2007.

His service was of an "exemplary nature" until his suspension in September 2013.

After that he was at a "significant monetary loss," Ms Leader said.

"I appreciate that this has been a very difficult matter for Mr O'Brien," Judge Smyth said.

"I think the court has no alternative but to proceed to conviction."

When interviewed by GSOC, O'Brien denied any involvement in sending the envelope. He said he knew the alleged sender through her father and had not spoken to her since the 1990s.

Around January 2011, he met her father and told him he was "working with a 'p***k" - Det Sgt Buckley, who was "making my working conditions unbearable."

He did not ask the man to do anything and did not know his daughter was going to send the card. He said he had never threatened Det Sgt Buckley or his family, but had made two bullying complaints about him and believed this was the motivation behind the GSOC complaint.